The present invention relates to a method of removing mercury as a simple substance and/or mercury compounds (hereinafter often referred to as "mercury and its compounds") which is or are present in hydrocarbon oils.
For reforming hydrocarbon oils such as naphtha by, for example, hydrogenation, such catalysts as palladium catalyst supported on alumina are used. On the other hand, if mercury and its compounds are present in hydrocarbon oils as impurities, such reaction as hydrogenation cannot be carried out sufficiently due to the catalyst poisoning caused by such impurities.
Therefore, the following methods have been conventionally practiced for the removal of mercury and its compounds:
(a) Physical adsorption methods for which porous adsorbents such as activated carbon, molecular sieve, silica gel, zeolite, and alumina are employed.
(b) Methods of removing mercury and its compounds by reaction between mercury and sulfur or adsorption by means of using metal sulfides or adding sulfur to a porous adsorbent.
However, the physical adsorption method mentioned in (a) above gives a low mercury removal ratio of 30 to 70 weight percent, whereas heavy fractions and gummy matter are removed efficiently from hydrocarbon oil. The reactive adsorption method mentioned in (b) above gives a low mercury removal ratio as is the case with the physical adsorption method (a), while filtration after the reactive adsorption step is made with great difficulty.
For the aforesaid reason, a strong need exists for developing a method that is capable of selectively and efficiently removing mercury from hydrocarbon oils.